A classification of techniques for the compensation of time delayed processes. Part 2: Structurally optimised controllers

Following on from Part 1, Part 2 of the paper considers the use of structurally optimised controllers to compensate time delayed processes

The design of linear multivariable control systems using modern control theory /with applications to coupled core reactor control/

Linear multivariable control system design using modern control theory, and application to coupled core reactor contro

Study of numeric Saturation Effects in Linear Digital Compensators

Saturation arithmetic is often used in finite precision digital compensators to circumvent instability due to radix overflow. The saturation limits in the digital structure lead to nonlinear behavior during large state transients. It is shown that if all recursive loops in a compensator are interrupted by at least one saturation limit, then there exists a bounded external scaling rule which assures against overflow at all nodes in the structure. Design methods are proposed based on the generalized second method of Lyapunov, which take the internal saturation limits into account to implement a robust dual-mode suboptimal control for bounded input plants. The saturating digital compensator provides linear regulation for small disturbances, and near-time-optimal control for large disturbances or changes in the operating point. Computer aided design tools are developed to facilitate the analysis and design of this class of digital compensators

TUNING PD AND PID CONTROLLERS VIA THE LAMBERT W FUNCTION FOR DOUBLE INTEGRATOR PLUS DEAD TIME PROCESSES

The paper explores the Proportional-derivative controller for a double integrator plus dead time processes, which is a challenging control problem, that is designed based on the existing Proportional-integrative controller for integrator plus dead time processes. The PD controller is extended with an integral action and an ideal PID controller is received. The parameters of both controllers are received by using the pole placement technique, whereby the transcendent characteristics equation of the closed loop system is solved by using the Lambert W function. The paper also examines the influence of the desired poles of the system with a closed feedback as well as the influence of the disturbance and the change of the DIPTD processes parameters onto the received control system performances. The results received by simulation, and the quantitative indicators, show that the proposed control system has better performances in comparison to the control systems obtained by other methods in literature

Vibration control on linear robots with digital servocompensator

Control application for active damping of structural vibrations and acoustic noise in mechanical systems is one of the engineering fields that can benefit from advances made in digital signal processors. This thesis project is one such application. It is about a vibration control at the loading point of a high speed linear robotic workcell. A lead zirconate titanate piezoelectric ceramic is used as the actuator and an accelerometer provides the sensing. From experimentally measured frequency response of this system, a shaping filter is designed and added on. The reshaped system is fitted with a third order transfer function design model. And based on this model, a discrete-time control scheme designated “servocompensator” is designed and implemented on a Digital Signal Processing board to control structural vibrations on the robotic workcell. Servocompensator is a control scheme based on the principle of Internal Model Design. The results have demonstrated the servocompensator as a powerful scheme for controlling independently the individual modes within the spectrum of a given vibration signal. In a typical result, as much as 40 dB of attenuation is produced on the targeted mode, where 0 dB is equal to 1 g of acceleration in this application. Furthermore, with the multi-tasking capability of the digital hardware, multiple mode control is demonstrated by multiplexing a number of single-mode servocompensators

Intelligent control of nonlinear systems with actuator saturation using neural networks

Common actuator nonlinearities such as saturation, deadzone, backlash, and hysteresis are unavoidable in practical industrial control systems, such as computer numerical control (CNC) machines, xy-positioning tables, robot manipulators, overhead crane mechanisms, and more. When the actuator nonlinearities exist in control systems, they may exhibit relatively large steady-state tracking error or even oscillations, cause the closed-loop system instability, and degrade the overall system performance. Proportional-derivative (PD) controller has observed limit cycles if the actuator nonlinearity is not compensated well. The problems are particularly exacerbated when the required accuracy is high, as in micropositioning devices. Due to the non-analytic nature of the actuator nonlinear dynamics and the fact that the exact actuator nonlinear functions, namely operation uncertainty, are unknown, the saturation compensation research is a challenging and important topic with both theoretical and practical significance. Adaptive control can accommodate the system modeling, parametric, and environmental structural uncertainties. With the universal approximating property and learning capability of neural network (NN), it is appealing to develop adaptive NN-based saturation compensation scheme without explicit knowledge of actuator saturation nonlinearity. In this dissertation, intelligent anti-windup saturation compensation schemes in several scenarios of nonlinear systems are investigated. The nonlinear systems studied within this dissertation include the general nonlinear system in Brunovsky canonical form, a second order multi-input multi-output (MIMO) nonlinear system such as a robot manipulator, and an underactuated system-flexible robot system. The abovementioned methods assume the full states information is measurable and completely known. During the NN-based control law development, the imposed actuator saturation is assumed to be unknown and treated as the system input disturbance. The schemes that lead to stability, command following and disturbance rejection is rigorously proved, and verified using the nonlinear system models. On-line NN weights tuning law, the overall closed-loop performance, and the boundedness of the NN weights are rigorously derived and guaranteed based on Lyapunov approach. The NN saturation compensator is inserted into a feedforward path. The simulation conducted indicates that the proposed schemes can effectively compensate for the saturation nonlinearity in the presence of system uncertainty

Design, analysis and control of DC/DC converter based DC wind farms

This thesis discusses the design, operation and control of DC wind farms that use high power DC/DC converters, DC cables and DC collection networks. DC wind farms are proposed as alternatives to traditional AC wind farms due to the potential to reduce the system size, improve the speed of dynamic response and improve the system efficiency. DC wind farms involve different types of high-power DC/DC converters in different stages of power conversion. Isolated DC/DC converters are chosen as the wind turbine converters in which the intermediate transformer design is of great importance. A general and comprehensive medium frequency transformer modelling and design methodology is presented in this thesis, which considers the efficiency, leakage inductance and thermal management. The proposed methodology is applied to transformers for single phase and three phase DC/DC converters. Isolated Single Active Bridge DC/DC converters are appealing topologies for medium voltage applications. The operation of these DC/DC converters is complex and important for the converter control design. The comprehensive operational principles of three-phase single active bridge converters under changing duty cycle are investigated. Eight operating modes are identified with detailed derivation of power flow and current dynamics. The converter performances are evaluated and compared theoretically and experimentally. Then, the control of wind turbine converters in DC wind farms is designed considering both DC-link and network dynamics. To deal with the oscillations caused by smoothing reactors, a power system stabilizer based control design is developed and implemented. Furthermore, a multi-variable feedback control design using pole-placement technique is proposed. This method is able to achieve the minimum oscillatory time without compromising the dynamic performance of the DC-link voltage. Finally, taking into account the low capacitance issue in wind farms, the voltage stability of DC wind farms is investigated and different stabilizing methods are designed and analyzed. The impedance models of aggregated wind turbine converters, DC cables and the station DC/DC converter with control action are derived, in order to study the interactions between the station converter and the DC wind farm. A new equivalent capacitor control strategy to enhance the system capacitance is proposed and analyzed through various case studies.Open Acces

Design and analysis of lunar lander control system architectures

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Aeronautics and Astronautics, 2012.Cataloged from PDF version of thesis.Includes bibliographical references (p. 153-157).Although a great deal of separate work exists on the development of spacecraft actuators and control algorithm design, less work exists which examines the connections between the selection of specific actuator types and placements, how this affects control algorithm design, and how these combined factors affect the overall vehicle performance of a lunar lander. This thesis attempts to address these issues by combining a functionality-oriented approach to actuator type/placement with a controls-oriented approach to algorithm design and performance analysis. Three example control system architectures are examined for a generic autonomous 350kg lunar lander during the terminal descent flight phase. Results indicate that stability and control can be achieved using a wide variety of actuator types/placements and algorithms given that a set of 'common sense' subsystem functionality and robustness metrics are met; however, algorithm development was often heavily influenced/restricted by actuator system capabilities. It is therefore recommended that future designers of lunar lander vehicles consider the impact of their control system architectures from both a functionality-oriented and a controls-oriented approach to gain a more complete understanding of the effects of their choices on overall performance.by Joseph M. Morrow.S.M

Five-Level Flying Capacitor Converter used as a Static Compensator for Current Unbalances in Three-Phase Distribution Systems

This thesis presents and evaluates a solution for unbalanced current loading in three-phase distribution systems. The proposed solution uses the flying capacitor multilevel converter as its main topology for an application known as Unbalanced Current Static Compensator. The fundamental theory, controller design and prototype construction will be presented along with the experimental results. The Unbalanced Current Static Compensator main objective is the balancing of the up-stream currents from the installation point to eliminate the negative- and zero-sequence currents originated by unbalanced single-phase loads. Three separate single-phase flying capacitor converters are controlled independently using a d-q rotating reference frame algorithm to allow easier compensation of reactive power. Simulations of the system were developed in MATLAB/SIMULINK™ in order to validate the design parameters; then, testing of the UCSC prototype was performed to confirm the control algorithm functionality. Finally, experimental result are presented and analyzed